VISUAL AGING

Visual Aging (Optical Factors)

As we age, changes in the visual system begin to affect our ability to carry out everyday tasks. For some individuals the changes can be severe. Approximately half of the people in North America who are legally blind (corrected acuity worse than 20/200 and/or visual fields of 20 deg or less) are 65 or over, as are about two-thirds of those with severe visual impairment (inability to read newspaper print with best correction). Fortunately, normal age-related visual changes are much less dramatic.

Changes in the optical media of the eye attenuate, scatter and alter the spectral composition of the light reaching the retina. The pupil decreases in size with aging, a change called senile miosis. This reduces the light entering the eye. The lens also hardens (lenticular sclerosis) and yellows, further reducing the light reaching the retina, especially from the blue end of the visible spectrum. Changes in the lens also increase light scatter, which reduces light/dark differences (i.e., contrast) in the image. By age 60, it is estimated that the retina receives only about one-third as much light as a 20-year old eye. About two-thirds of this loss is due to a smaller pupil, the other one-third to changes in the lens.

How Does Aging Affect Visual Function?

Age-related optical changes in the eye have several adverse effects on visual functioning. Acuity, our ability to see fine details, declines. This is especially true under conditions of low illumination. In addition, generally we need more contrast to detect or recognize stimuli, especially if they are small. Older persons are also more disadvantaged by glare conditions. Hardening of the lens reduces the eye’s ability to accomodate, that is, make the lens more spherical and thus increase its refractive power for focusing on nearby objects. This change, called presbyopia, (“old eye”), results in an age-related recession of the near point, the closest distance for clear vision. At age 20, the average person can focus as close as 10 cm.; this increases to 22cm at age 40 and to 100 cm by age 60. The visual effects of this progressive change usually become noticeable by about age 45, which explains why older people are often seen holding their reading material at arm’s length.

The photos (below) approximate a view of a traffic scene in a young observer and an elderly observer. Notice the decreased luminance and clarity in the second photo.

 

Treatment

Older observers benefit from visual materials that are of high contrast, larger size and presented in good non-glare lighting conditions. Tasks involving low light levels or subtle discriminations between different shades of blue should be avoided. Presbyopia is treated using convex (positive sphere) corrective lenses to compensate for the older eye’s inability to increase its refractive power for near stimuli. This can take the form of reading glasses or by the addition of a positive sphere component to the lower part of the person’s regular eyeglasses (i.e., bifocal, trifocal or multifocal lenses).

EXPLORE VISUAL AGING: REMBRANDT?